Apparatus for the electrolysis of alkali metal salts and process therefor



1959 SHOGO FUJIOKA ETAL 2,916,425 APPARATUS FOR THE ELECTROLYSIS of"ALKALI METAL SALTS AND PROCESS THEREFOR 2 Sheets-Sheet 1 Filed May 28,1958 Dec. 8, 1959 SHOGO FUJIOKA ETAL APPARATUS FOR THE ELECTROLYSIS OFALKALI METAL SALTS AND PROCESS THEREFOR 2 Sheets-Sheet 2 Filed May 28,1958 United States Patent APPARATUS FOR THE ELECTROLYSIS OF ALKALI METALSALTS AND PROCESS THEREFOR Shogo Fujioka and Seiji Yoshida, Osaka,Shotaro Terasawa, Amagasaki, and Osamu Shiragami, Toyonaka, all ofJapan, assignors to Asahi Garasu Kabuslnki Kaisha, Tokyo, Japan, acorporation of Japan Application May 28, 1958, Serial No. 738,356 Claimspriority, application Japan June 1, 1957 5 Claims. (Cl. 20468) Thepresent invention relates to apparatus designed for the electrolysis ofsolution of alkali metal salts, especially alkaline chlorides such assodium chloride and the like, with the aid of mercury electrode andprocess therefor.

It is an object of this invention to provide a remarkably improvedelectrolytic apparatus or electrolyser as compared with the conventionalelectrolytic apparatus.

It is possible according to the present invention to provide anelectrolytic apparatus having various advantages, such as the requiredamount of mercury is extremely small and the electrolysis can be carriedinto effect at a high current density but low voltage, and the like,which result from the fact that mercury is forcedly caused to flow andspread in all directions on a revolving metallic disc in the form of athin layer.

According to this invention, mercury is fed on a metallic disc rotatablein a horizontal position, said mercury being forcedly caused to flow inall directions in the form of thin layer on the said disc while flowingthereon due to the centrifugal force of the revolving metallic disc,while a solution of alkali metal salt is submitted to the electrolysisbetween said mercury layer as cathode and an anode arranged in oppositeand above to said mercury layer. Therefore, there is an advantage thatthe necessary quantity of mercury in an electrolyser or electrolyticcell is remarkably small. In addition, because of mercury being causedto flow and widen in the form of uniform thin layer, not only thespacing between both cathode and anode can be made small, but also theelectrolyte solution is caused to flow and widen with stirring at highvelocity by the revolution of the metallic disc. Thus, gas such aschlorine gas evolved on the lower face of the anode can be quicklydispersed. Consequently, the rise of the electrolytic voltage will below even when the electrolysis is carried out at a high current density.It is possible, therefore, to perform the electrolysis at a high currentdensity and, accordingly, the current efficiency is increased.

Furthermore, according to this invention, the mercury is forcedly causedto flow over the rotating metallic disc and the flowing movement of themercury is favorably effected with stirring as described above.Accordingly, the allowable limitation for calcium and magnesium saltswhich are contained in the electrolyte solution becomes wider, leadingto a decrease in the refining cost on account of a simple refining stepof the electrolyte. Moreover, as described above, the flowing movementof mercury is performed satisfactorily, with the result the surfacialconcentration of mercury amalgam being low and being capable ofoperating at low voltage, and the increase of current density as well asthe improvement in current efiiciency can be obtained. Furthermore, afurther advantage of this invention resides in that the head of mercuryin the electrolyser or electrolytic cell can be made remarkably low.Because of various advantageous features as set forth above, a small,but extremely high ice electrolytic capacity can be obtained in thisinvention, whereby the floor area of the electrolytic cell is small withlow construction and equipment costs.

Other objects, features and advantages of the present invention will beapparent from the following descriptions given with reference to theaccompanying drawings.

In order that the present invention may be more clearly understood andreadily carried into effect, three examples of the embodiment of thisinvention will now be described, by way of example, with reference tothe accompanying drawings, in which:

Fig. 1 is a longitudinal sectional view of an embodiment of theelectrolyser or electrolytic cell according to this invention;

Fig. 2 is a plan view thereof, partially broken away;

Fig. 3 shows diagrammatically a longitudinal sectional view of anotherembodiment of electrolyser of a type wherein the electrolyser asillustrated in Figs. 1 and 2 are heaped one above another; and

Fig. 4 is a longitudinal sectional view showing a further embodiment ofan electrolyser according to this invention.

Referring to Figures 1 and 2, a circular opening or bore 2 is formed atthe center of an iron disc 1 horizontally positioned. A vertical hollowshaft 3 is secured at the disc shaped base 4 of its bottom end to aperipheral edge of said circular opening 2 by a suitable manner, forinstance, welding or bolting and the like. The said shaft 3 is supportedby a bearing (not shown in the drawings) and revolved by an appropriatedriving means, thereby said iron disc 1 being horizontally positionedand revolved at 20100 r.p.m., for instance. Further, the upper face ofsaid iron disc 1 may be horizontally machined, or inclined somewhattowards the outer periphery, or the said face may also be made as acurved surface. Moreover, these faces are usually finished smooth, butif necessary, a groove may be formed, or iron wires or nets may besecured thereto by welding in order to increase the surface area, whichis permitted in cases where no obstacles exist. All these features areincluded within the scope of the present invention.

The aforesaid iron disc 1 is formed with the bent portion 6 bydownwardly bending the circumferential edge portion throughout the wholecircumferential portion of said disc.

The anode 7 made of a well-known material such as a graphite and thelike is arranged above and oppositely to said iron disc 1 at the desiredspacing thereto. This anode 7 is arranged in opposition to and abovesaid iron disc 1 at the required spacing to said disc as set forthabove. The anode 7 whose section is shown in Fig. 1 is a graphite dischaving approximately the same diameter as said iron disc 1, and can bemade of a single block of graphite material, or formed from an assemblyof suitable shaped graphite blocks.

The anode '7 is carried in an ascendable and descendable manner on acover plate 9 of an iron electrolytic cell 3, which includes theabove-mentioned iron disc 1 and the anode 7, in the well-known manner.The position of said anode '7 is designed to be adjustable in accordancewith the abrasion of anode 7 on its lower end face. 10 represents ananode lead of said graphite anode 7. Moreover, the iron electrolyser 8is formed in the cylindrical form and bottom portion 11 thereof isformed in the conical form. In the joining portion between thecylindrical and conical portions of the electrolyser body an amalgamtrap 12 is provided along the entire inside periphery. The said amalgamtrap 12 comprises an overflow wall (12 surrounding the entire peripheryof the conical body in order to reserve the amalgam therein.

The bent portion 6 of flange of said iron disc 1 extends to such aposition that said bent portion 6 is immersed in the amalgam retained inthe said amalgam trap 12, thereby the cylindrical body of electrolyserand the conical bottom body 11 are sealed by the said amalgam. Thus, theelectrolyser body is divided with said sealing into an amalgamatingchamber 13 of the cylindrical body and an amalgam decomposition chamber14 below.

Further, the cover plate 9 of the electrolyser 8 is respectivelyprovided with one or more feed pipes 15 for an alkaline salt solutionand outlet pipes 16 for generated gas. Moreover, a suitable number ofoutlet pipes 17 for a depleted alkali metal salt solution or anelectrolysed waste solution is fitted around the cylindrical wall of theamalgamation chamber 13, i.e. the upper half cylindrical portion ofelectrolyser 8.

The upper cylindrical wall of electrolyser 8, i.e. side wall ofamalgamation chamber 13 is lined on its inner surface with corrosionresistant and electrical insulating material such as polyethylenechloride trifluoride (not shown). In particular, said lining extends tothe lower end of the amalgam trap 12, and on the lining portion of saidtrap a thin iron plate is preferably set.

The bottom portion of electrolyser 8, i.e. the portion following to thelower end of the amalgam trap is conical as described above, the bottomwall 11 sloping toward the middle, said middle portion being formed witha recess 17, and the said recess serves as a mercury reservoir. Amercury pump 18 is immersed at its bottom end in the mercury in saidmercury reservoir 18 (refer to Fig. 1). The mercury pump 18 is rotatedby means of the revolving shaft 19 arranged in the hollow revolvingshaft 3 of the said iron disc 1 and secured at its bottom to a rotator20 of said pump 18. Said mercury pump as represented in Fig. 1 is of aninverted truncated cone shape with its top being cut olf. Between thecasing of said pump 18 and the outer surface of the inner rotator 20 isformed a narrow conical space. This rotator may also be provided withblades, if necessary. The mercury is sucked up along the said space withthe revolution of the pump. The top face of said pump is previouslypositioned at substantially the same level as the upper face of the irondisc 1 or somewhat lower than the said upper face. Thus sucked-upmercury is supplied to the upper surface of the iron disc 1 through asmall hole provided in the portion for connecting the iron disc 1 andthe disc shaped base 4 of the hollow revolving shaft 3. The surface ofbottom wall 11 of the amalgam decomposition chamber 14 is convenientlyprovided with a number of blocks of amalgam decomposing material 21 madeof, for instance, a graphite or sintered material of iron and graphite.For instance, they are preferably arranged radially at the suitablespacing around the mercury reservoir as a center and secured on thebottom plate 11 with wire gauzes and the like. The amalgam overflowingfrom amalgam trap 12 flows down among said blocks of the amalgamdecomposing material 21, in the course of which said amalgam isdecomposed by amalgam decomposing water. An inlet pipe 22 for amalgamdecomposing water and another outlet pipe 23 for discharging a causticalkali produced by the decomposition of amalgam are respectivelyinserted from below through the bottom wall 11 of said amalgamdecomposing chamber 14 and these pipes 22 and 23 open respectively at adesired level in said chamber. From this pipe 22 is introduced theamalgam decomposing water and the amalgam is decomposed to producecaustic alkali. The formed caustic alkali is discharged from the outletpipe 23 together with the resulting hydrogen gas. Thereafter, thehydrogen gas may be separated from the caustic alkali. The mercuryproduced by the decomposition of amalgam is sucked up from the mercuryreservoir 18 by the mercury pump 18 as referred to above, and fedthrough the aforesaid small hole 5 again on the iron disc 1 and forcedlyspread in all directions on the surface of the said disc in the form ofthin layer under flowing thereon due to the centrifugal force of therevolving iron disc 1, and the electroyte solution introduced from inletpipe 15 for alkali metal salt solution is electrolysed between the anodeand the cathode of the thin mercury layer, the resulting amalgamcollecting in the amalgam trap. 12. On the other hand, the electrolysedwaste solution is discharged from the outlet pipe 17, and circulatedagain as is wellknown after alkali metal salt is dissolved therein. Theconnection between the present electrolyser and an electric source (notshown in the drawings) is performed in such a manner that the anodecurrent is connected from the electric source to the anode lead and thecathode bus bar is connected with the bottom plate of the amalgam trap12 and the cathode current is connected to the mercury flowing down onthe iron disc 1, thus a circuit is created. Further, alkali metal saltsolution may be, if necessary, supplied from the upper enlarged portion24 of the hollow revolving shaft 3.

As shown in the plan view, Fig. 2, the amalgam trap 12 is formed with anamalgam butter box 25 by extending the end of said trap 12 in thetangential direction of the cylindrical portion of the electrolyser.Thus, amalgam butter or anodic disintegratings formed during theelectrolysis collect in said box 25, the amalgam butter and thedisintegratings being conveniently drawn out through the opening 26.

Fig. 3 illustrates, by way of example, an electrolyser of a. type,wherein an electrolyser or electrolytic cell as shown in Figs. 1 and 2is superposed in three rows, and which differs from the electrolyser ofFig. 1 only in that without providing a mercury pump 18 as describedabove at the middle inside of each electrolyser in order to transmit themercury consecutively from the upper cell to the next lower one, andfrom the lowest or the third cell the mercury is recycled to the firstcell by means of a pump installed outside of the electrolysers.

Such an arrangement as set forth above is more effective in order toreduce the floor area of the electrolyser.

In Figure 3, numerals 27, 28 and 29 are respectively iron discs, each ofwhich is mounted on the revolving shaft 30 and revolves at thepredetermined velocity.

31, 32 and 33 represent all anodes respectively. Mercury is first fedthrough inlet pipe 34 and supplied on the iron disc 27 in anamalgamation chamber 63 of the first row of the electrolyser 41 througha pipe 35 surrounding the outside of the revolving shaft 30. Then, themercury is forcedly spread, under flowing on the iron disc in the formof a thin layer over the surface of the disc 27 through the centrifugalforce due to the revolution of said disc 27, and the electrolysis iseffected between the cathode of the thin mercury layer and the anode 31.Alkali metal salt solution to be electrolysed may be fed from themercury inlet pipe together with the mercury, or an inlet pipe thereformay be separately provided. Amalgam thus produced is collected in theamalgam trap 36. This amalgam trap 36 has a similar construction as thatdescribed in connection with Figs. 1 and 2. The amalgam over-flown fromthe said amalgam trap flows down among a number of blocks of amalgamdecomposition material 38 in the amalgam decomposition chamber 37, inthe course of which said amalgam is decomposed by the amalgamdecomposing water and collected in the mercury reservoir 39. In thismercury reservoir 39, there is provided a cover 40, the lower end ofwhich is immersed in the mercury of said mercury reservoir, thereby theamalgam decomposition chamber 37 of electrolyser 41 of the first row aswell as the amalgamation chamber 64 of electrolyser 42 are arranged tobe sealed with the mercury of the said reservoir 39. The cover 40 forsealing may be mounted on the revolving shaft 30 or secured to thebottom wall of amalgam decomposition chamber 37. The mercury over-flowsfrom the over-flowing wall 44 through the lower end of said cover 40 andflows down to the iron disc 28 of the second row. The electrolyser 42 ofthe second row has a similar construction as that of .electrolyser 41 ofthe first row, and the mercury becomes amalgam on the iron disc 28 andcollected in amalgam trap 45, from which the amalgam over-flows in theamalgam decomposition chamber 43 and is decomposed by amalgamdecomposing water under flowing among a number of blocks of amalgamdecomposing material 46 and collected at a mercury reservoir 47. Mercuryoverfiown a over-flow wall 61 of said reservoir 47 is fed from here ontothe iron disc 29 into an amalgamation chamber 62 of electrolyser 48 ofthe third row similarly as in the case with said mercury reservoir 39.Thus, mercury flows over the disc 29, collected in an amalgam trap 49after having become amalgam further over-flows and then flows down amonga number of blocksof amalgam decomposing material 59 in an amalgamdecomposition chamber 52 of electrolyser 48 of the third row and isdecomposed and then collected in the last mercury reservoir 51 ofelectrolyser 48 of the third row. The mercury collected here is recycledto the mercury feeding opening 34 by means of a mercury pump 53 througha feed pipe 54. Each of amalgam decomposition chambers 37, 43 and 52 isrespectively provided with feed pipes 55, 56 and 57 for amalgamdecomposing water and outlet pipes 58, S9 and 60 for caustic alkaliproduced in the electrolysis.

In the amalgamation chambers 63, 64 and 62 of the first, second andthird rows, there are respectively provided feed pipes for alkali metalsalt solution and outlet pipes for electrolysed waste solution in asuitable manner although they are not shown in the drawings. The outletpipes for discharging gas generated in the amalgamation chambers arealso arranged respectively in suitable positions though they are notshown in the drawings. The anode lead rods 66, 67 and 68 are connectedwith anode laterally of each respective electrolysers. In the cathodeconsisting of the thin mercury layer, a cathode current is fed to themercury layer by connecting a cathode bus bar (not shown) with theamalgam trap.

A further another embodiment of this invention as shown in Fig. 4 willhe explained.

The electrolyser illustrated in Fig. 4 has a further simple constructionas compared with those illustrated in Figs. 1 and 2 may be regarded asone adapted as an independent unit from those types illustrated in Fig.3. Namely, a mercury pump is arranged outside of the electrolyser inorder to circulate the mercury outside the cell. Namely, theelectrolyser body, as in the said Figs. 1 to 3, consists of acylindrical portion 69 and a conical portion 70, the bottom portionthereof being made of iron, said cylindrical portion 69 constitutes anoutside wall of an amalgamation chamber 71, and the said conical portion70 constituting the bottom wall of an amalgam decomposition chamber 72.The cylindrical portion 69 of said electrolyser is lined on the innerface thereof with a corrosion resistant and electrical insulatingmaterial such as polyethylene chloride tri-fiuoride resin, and the like.Said lining is so extended that it may also line the inner face ofamalgam trap and a thin iron plate is preferably set on the liningportion of the said trap as described hereinbefore. Like the cases withsaid Figs. 1 to 3, the iron disc 73 has its circumferential edge portionbent downward, said iron disc 73 being so positioned that the disc mayconstitute the bottom plate for the amalgamation chamber 71, said disc73 being carried by the revolving shaft 74 secured to the lower face ofthe middle of said disc and simultaneously designed to be revolved by anappropriate driving means (not shown) through said revolving shaft 74.The surface of the iron disc 73 may also be inclined towards itsperiphery or may have a curved face similarly as in the case of theelectrolyser illustrated in Figs. 1 and 2. In the middle portion of thesurface of said iron disc 73 is formed a circular recess 75, andmercuryis designed feed pipe 76 is hung down from above through thecover plate 77 of the electrolyser and is opened with its bottom end ata position slightly apart from the surface of said recess 75. Inside themercury feed pipe 76 is fitted an iron plate having a number of smallperforations (not shown). The mercury which is fed to the recess 75 ofthe iron disc 73 is arranged advantageously to be supplied in the formof small drops after passing through said small perforations. Further,the cover plate 77 of electrolyser is fitted with a feed pipe 78 foralkali metal salt solution such as, for instance, sodium chloridesolution, through which the alkali metal salt solution is fed to theamalgamation chamber 71. To the side wall 69 of the amalgamation chamber71 is secured an outlet pipe 79 for an electrolysed waste solution,through .which the waste solution is drawn out after the electrolysishas been elfected. Thereafter, as is well-known, said solution is againcirculated after alkali met-a1 salt has been dissolved therein. On thecover plate 77 of electrolyser an outlet pipe 80 for gas generated inthe amalgamation chamber 71 is secured separately. Gas generated duringthe electrolysis at the anode, for instance, chlorine gas is drawn outtherefrom. Beneath the peripheral edge of iron disc 73 there is providedan amalgam trap 81 along the entire circumference of the cylindricalbody 69 of the electrolyser. This amalgam trap 81 is so constructed thatamalgam may be reserved up to a certain predetermined level by means ofan inner wall 82 having over-flow notches 93.

Further, a bent portion 83 of peripheral edge of the iron disc 73 andthe wall 82 are so designed that the bottom end of said bent portion 83may be immersed in amalgam of the amalgam trap 81. Thus, theamalgamation chamber 71 and amalgam decomposition chamber 72 of thepresent electrolyser are sealed with amalgam in the amalgam trap 81,thereby preventing the electrolyte solution of the amalgamation chamber71 from flowing into the amalgam decomposition chamber 72. The anode 85is made of well-known anode material, such as graphite as described inFig. 1 and formed at its middle with a circular opening or bore 84,through which a mercury feed pipe 76 centrally extends. The size of saidanode is such that its outer radius is substantially similar to that ofthe iron disc 73. This graphite anode is also provided with a graphitelead 86. In the accompanying drawings, though it is not shown, thisanode 85 with graphite lead 86 is supported in a usual supportingmanner, and simultaneously connected with the source of electric currentin order to conduct the anode current therethrough. For the cathodecurrent a cathode bus bar 94 is connected with the bottom plate of theamalgam trap 81, and the mercury is supplied from the mercury feed pipe76 to the recess 75 of said revolving iron disc 73. The mercury thussupplied to the recess 75 is forcedly spread in all directions on saidiron disc 73 in the form of a uniform thin layer under flowing thereonby the centrifugal force due to the revolution of said disc, while theelectrolysis of alkali metal salt solution is effected between the anodeand the cathode of the thin mercury layer and the mercury becomesamalgam and collects in the amalgam trap 81. Thus, the amalgam collectedin the amalgam trap overflows from the over-flow notches 93 of theover-flow wall 82 and enters in the amalgam decomposition chamber 72 andflows down along the bottom Wall thereof. The amalgam decompositionchamber 72 is conical as referred to above and has an inclined bottomwall 70 sloping down toward the center. An inlet pipe 87 for amalgamdecomposing water extends through the inclined bottom wall 70 of saidamalgam decomposition chamber from below and opens to the interior ofthe amalgam decomposition chamber 72, and an outlet pipe 88 for producedcaustic alkali solution is also secured to the inclined bottom wall 70of said amalgam decomposition chamber. These two pipes 87 and 88 openrespectively to appropriate levels inside the amalgam decompositionchamber 72. On the upper face of the said inclined bottom wall 70 aresuitably disposed a number of blocks of amalgam decomposing materials89. As the amalgam decomposing material, a well-known material, forinstance, a graphite or sintered material of graphite and iron, and thelike are used. These blocks of amalgam decomposing materials 89 arerespectively held, for instance, by a fitting piece secured to theinclined bottom wall 70 of the amalgam decomposition chamber 72. Theamalgam over-flown from the overflow notches 93 of the over-flow wall 82of the amalgam trap 81 passes through among said blocks of the amalgamdecomposing materials 89 and flows down toward the center of amalgamdecomposition chamber 72, in the course of which the amalgam isdecomposed by the amalgam decomposing water fed from the feeding pipe87. Caustic alkali solution thus then formed is drawn out of the outletpipe 88 together with generated hydrogen gas, and then said hydrogen gasis separated in a suitable manner. A mercury reservoir 90 is formed atthe center of the bottom of the amalgam decomposition chamber 72, amerury outlet pipe 91 is connected to said mercury reservoir 90.

The mercury, which is obtained from the decomposition of the amalgam inthe amalgam decomposition chamber 72, flows down said chamber and iscollected first in the mercury reservoir 90 and discharged through themercury outlet pipe 91 and then recycled to the amalgamation chamber bymeans of a pump (not shown). At the underside of said iron disc 73 arefitted any suitable number, for instance, a few stirring blades 92 inorder to promote the decomposing action, two of which are shown in Fig.4. Also in this electrolyser, though not shown, the amalgam trap extendstangentially to the cylindrical body 69 of the electrolyser toconstitute an amalgam butter box similarly as in the case of theelectrolyser shown in Figs. 1 and 2. The amalgam thus produced in thecell is arranged to collect in said amalgam butter box and to be drawnout by any convenient manner.

The number of revolutions of the iron disc in the electrolyser orelectrolytic cell of the aforesaid embodiments varies depending on thediameter of the said disc and other conditions. In general, 20 to 100r.p.m. are satisfactory. However, the optimum number of revolutions maybe selected in each case. For instance, it has been found from theresult of the experiments effected with respect to the electrolyser ofthe type illustrated in Fig. 4 that in the case where a mild steel dischaving a diameter of 530 mm. and a thickness mm. is used and a recesshaving a diameter of 70 mm. and a depth of 3 mm. is formed at the centerof the bottom wall wherein the mercury is fed at a rate of 3 litres perminute, and sodium chloride solution is electrolysed, a satisfactoryresult is obtained at around 20 to 100, preferably 40 to 60 revolutionsper minute.

In the said experiment, the mercury running on the iron disc may runsmoothly in the form of a thin layer of below 0.5 mm. Accordingly, thespacing between the anode and cathode may be extremely small.Furthermore, from the result of this experiment, it has been found thateven a minimum spacing of 1.3 mm. permits satisfactory electrolysis.However, with a little allowance a practical operation was carried outat the spacing of 3 mm., with extremely favorable results. Because ofthe above possibility of small clearance, the electrolytical voltage canbe made remarkably low. Consequently, the electrolysis can be effectedat a high current density. Thereby, the current efficiency is remarkablyincreased.

The result of the electrolysis effected in the electrolyser having aniron disc of 530 mm. in diameter under the following conditions is, byway of example, shown as follows:

Current efflclency Voltage Current density (Amp/din!) (Volt) (percent)Further, when an impure sodium chloride solution containing 1 g./l. ofCaO such as calcium salt and 500 mg./l. of MgO as magnesium salt waselectrolysed similarly in the same electrolyser, a smooth operationcould be continued without any obstructions. The hydrogen gas in thechlorine gas generated at the time was below 0.5%. In a 25,000 amp.electrolyser, the diameter of the iron disc may be 1800 mm. and thethickness may be 15 mm. In this instance, the total mercury amountthroughout the amalgamation chamber, the amalgam decomposition chamberand other pipings was 250 kg. The floor area of the electrolyser was 9m. for caustic soda 1 metric ton/day in a caustic soda electrolyticplant of 2000 metric tons/month. Both values were remarkably small ascompared with those in the usual electrolyser.

The electrolyser or electrolytic cell according to the present inventionis by no means restricted by the foregoing descriptions of theembodiments. For instance, the electrolyser may be provided with asuitable stirrer for the electrolyte of the amalgamation chamber.Moreover, the anode may be so constructed that it may be rotated in thesame or reverse direction with the iron disc. On the other hand, theamalgam decomposition chamber is not limited to the type described inthe foregoing embodiments, and the amalgam decomposition chamber asshown in Fig. 4 may be used merely as a passage for amalgam. It is alsowithin the scope of the invention to permit the amalgam to be drawn outof the electrolytic cell and introduced into a separate amalgamdecomposition cell, such as a vertical type amalgam decomposition cell,and then decomposed therein.

T-hese modifications are included within the scope of the presentinvention.

Furthermore, the following types of amalgam decomposition cells may alsobe used. Namely, the revolving iron discs as set forth hereinbefore maybe used similarly for the decomposition of the amalgam. That is, an irondisc may be similarly revolved, on which amalgam is fed, and the amalgammay now be caused to widen on the disc under flowing thereon in the formof a thin layer due to its centrifugal force. An extremely good resultcan be obtained even when amalgam is decomposed while being fiown. As anamalgam decomposition cell wherein such an operation is carried out, anamalgam decomposition cell can be employed in which a revolving shaft issecured to one or more iron discs and a mercury feed pipe for feedingmercury on said iron discs; an inlet pipe for amalgam decomposing water;and an outlet pipe for discharging produced caustic alkali arerespectively provided and a counter-electrode is disposed directly orsomewhat apart from the said iron disc.

What we claim is:

1. Apparatus for the electrolysis of alkali metal salts, which comprisesa metallic disc rotatable in a horizontal position, an anode arrangedopposite the said metallic disc and thereabove, and a mercury feed pipefor feeding mercury to the central portion of said metallic disc, acathode being formed of a thin layer of mercury which is fed on therevolving metallic disc and spread in all directions on said disc in theform of a thin layer while flowing thereon by the centrifugal forceproduced due to the rotation of said metallic disc.

2. Apparatus for the electrolysis of alkali metal salts, which comprisesan electrolytic cell body consisting of a cylindrical upper half portionand a conical lower half portion, the upper half and the lower half ofwhich cell body form respectively an electrolytic chamber and an amalgamdecomposition chamber, a rotatable metallic disc so arranged as toconstitute the bottom portion of said cylindrical electrolytic cellportion and having a downwardly bent portion along the circumferentialedge, a mercury feed pipe disposed at the central portion of saidrotatable metal disc, an amalgam trap provided along the entire innerperiphery of the boundary portion between the said cylindrical upperportion the said conical lower portion of the electrolytic cell body,the bent portion of the aforesaid rotatable metal disc being dipped inthe amalgam collected in said trap, whereby the upper cylindrical halfportion and the lower conical half portion are sealed from each other,and a number of blocks of amalgam decomposing material arranged on aconical bottom wall of said lower half portion, whereby the amalgamover-flowing from said amalgam trap flows down along the inclined bottomwall of the said lower conical portion, in the course of which theamalgam is decomposed by means of amalgam decomposing water.

3. Apparatus for the electrolysis of alkali metal salts, wherein atleast two of the electrolytic cell body as defined in claim 2 aresuperposed vertically and the amalgamation is carried into effect in theupper electrolytic cell portion, and then the decomposed mercury istransferred to the lower electrolytic cell portion through a mercuryseal.

4. Apparatus for the electrolysis of alkali metal salts as claimed inclaim 2, wherein a mercury pump is provided at the central portion of anelectrolytic cell body, the lower end of said pump being dipped in amercury reservoir provided at the center of the bottom of the conicalamalgam decomposition chamber and the upper end thereof being positionedat substantially the same level as the face of a rotatable metallicdisc, whereby the mercury is adapted to be sucked up by the operation ofa pump, while the mercury obtained in the amalgam decomposition chamberis recycled to the rotatable metallic disc by a mercury pump disposedoutside the electrolytic cell.

5. A process for the continuous electrolysis of alkali metal salts whichcomprises the steps of producing a horizontal, radially flowing thinfilm of mercury by centrifugal action, flowing a horizontal, radiallyflowing film of alkaline metal salt solution upon said film of mercury,energizing said film of mercury to function as a cathode, arranging ananode directly above said mercury film to effect the electrolysis duringthe radial flowing of said mercury and metal salt films, collecting theproduced amalgam and contacting said amalgam with amalgam decomposingmaterial and solutions decomposing said amalgam and recycling themercury thus obtained to produce the aforementioned mercury film.

References Cited in the file of this patent UNITED STATES PATENTS646,313 Rhodin Mar. 27, 1900 705,264 Mactear July 22, 1902 FOREIGNPATENTS 1,020,965 Germany Dec. 19, 1957

5. A PROCESS FOR THE CONTINUOUS ELECTROLYIS OF ALKALI METAL SALTS WHICH COMPRISES THE STEPS OF PRODUCING A HORIZTONTAL, RADICALLY FLOWING THIN FILM OF MERCURY BY CENTRIFUGAL ACTION, FLOWING A HORIZONTAWL, RADIALLY FLOWING FILM OF ALKALINE METAL SALT SOLUTION UPON SAID FILM OF MERCURY ENERGIZING SAID FILM OG MERCURY TO FUNCTION AS A CATHODE ARRANGING AN ANNODE DIRECTLY ABOVE SAID MERCURY FILM OF EFFECT THE ELECTROLYIS DURING THE RADICAL FLOWING OF SAID MERCURY AND METAL SALT FILMS, COLLECTING THE PRODUCED AMALGAM AND CONTACTING SAID AMALGAM WITH AMALGAM DECOMPOSING MATERIAL AND SOLUTIONS DECOMPOSING SAID AMALGAM AND RECYCLING THE MERCURY THUS OBTAINED TO PRODUCE THE AFOREMENTIONED MERCURY FILM. 